1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a copier, and the like. More particularly, it relates to an image forming apparatus that includes replaceable units and is not supposed to have regular maintenance by a service person.
2. Description of Related Art
There have conventionally existed image forming apparatuses such as copiers, printers, and the like, that have a plurality of replaceable units, such as a print unit including a toner container and a photosensitive drum, a belt unit including an intermediate transfer belt, a primary transfer roller unit, a secondary transfer roller unit, a laser unit including a laser emitting apparatus, a fixing unit including fixing rollers, and the like. The above such units deteriorate as being used. Therefore, number of times to use a unit is counted to judge replacement timing. In case replacement timing is coming soon, or replacement timing has come, a user is alarmed of that fact through a display. FIG. 10 gives examples of replaceable units' names and respective life detecting means.
As to a copier or the like for office use, a service person generally checks and replaces a unit with new one any time. Therefore, in case any one of units for the copier reaches time for replacement, operation of the copier is immediately stopped in general. However, as to a printer or the like that is smaller and less complicated than a copier, a regular maintenance service contract is not arranged in many cases. Therefore, it is not preferable to stop operation of it forcedly. Accordingly, in many cases, unit replacement timing is just alarmed by indicating so in an operation panel. However, some users apt to overlook the alarm indication or even if users confirm the alarm indication, some of them keep using the printer while some fine images can be obtained.
In case a unit is kept being used over its replacement timing, e.g., in case toner residue alarm is neglected and the unit is kept being used, there may arise a fear that receipt of a facsimile message becomes impossible suddenly when toner is completely used out. Even for other units, e.g., in case an intermediate transfer belt is kept being used over its replacement timing, there may arise a fear that cracks appear on the belt and toner disperses inside the apparatus. Other than that, in case a print unit including a photosensitive drum is kept being used over its replacement timing, there may arise a fear that a bearing of the photosensitive drum gets worn out and the photosensitive drum rotates tremblingly. Under such a situation, a motor receives load larger than predetermined extent and life of the motor resultantly shortens.
Therefore, there have been devised various methods for surely notifying toner-near-empty state, to recommend a user to replace the toner cartridge. For example, Japanese Laid-open Patent Publications No. 1-133075, No. 9-160445, and No. 2001-56608 show examples of that. An electric photocopier apparatus directed to No. 1-133075 degrades its image density by reducing development width of its laser beam when toner residue lowers a predetermined amount. A recording apparatus directed to No. 9-160445 gets its printing density weaker by reducing printing dot pulse width when it gets into toner-near-empty state. Furthermore, in an electric photocopier apparatus directed to No. 2001-56608, LED chips are arranged on the back of its toner container so that light of the LED penetrates the container to generate a black line on paper when amount of toner lowers.
However, the above-mentioned respective prior techniques apply unique control methods for deteriorating an image so as to notify a user of unit replacement timing. What is more, additional parts are used for such unique control methods. Such aspects make system or structure of the apparatus complicated, which is problematic.